Low temperature refrigerator



1965 F. P. BROOKS LOW TEMPERATURE REFRIGERATOR Filed Jan. 22, 1964 3 Sheets-Sheet 1 INVENTOR.

FRANK P. BROOKS BY /aiz Edi/0% FIG.

ATTORNEYS Dem 1965 F. P. BROOKS LOW TEMPERATURE REFRIGERATOR 3 Sheets-Sheet 15 Filed Jan. 22, 1964 WQE .Q (D l!) i INVENTOR.

FRANK F? BROOKS ATTORNEYS United States Patent 3,222,877 LOW TEMPERATURE REFRIGERATQR Frank P. Brooks, 5 Inverness Road, Winchester, Mass. Filed Jan. 22, 1964, Ser. No. 339,399 Claims. (Cl. 626) This invention relate to a heat pump. More specifically, it relates to a mechanical heat pump having a plurality of tandemly arranged stages operating at successively decreasing temperatures. The system maintains the Working fluid in each stage in isolation from the working fluids in the other stages. This is accomplished by carrying out compression separately in each stage, including stages developing very low temperatures. It allows the lubricant and the working fluid for each stage to be selected for optimum efliciency according to the operating temperature of the stage.

Alternatively, in another arrangement, selected adjacent stages can use the same working fluid, thereby often simplifying construction. In any event, the lubricant, if any, is confined to a single stage and does not contaminate other stages.

Although the method and apparatus embodying the invention can be used for producing high temperatures, the invention is particularly suited for producing low temperatures and will be described accordingly.

In prior mechanical refrigerators, compression is carried out at elevated temperatures, even for stages that produce low temperatures. The lubricant required in high temperature compressors migrates into the low temperature portions of the refrigerator, often causing malfunctions. For example, lubricant that migrates into the low temperature portions can freeze and render the system inoperative or highly ineflicient.

Accordingly, it is an object of the present invention to provide an improved heat pump. More specifically, it is an object to provide an improved method and apparatus for producing low temperatures.

Another object of the invention is to provide a mechanical refrigeration method and apparatus in which lubricants do not interfere with low temperature operation.

Another object of the invention is to provide a mechanical heat pumping method and apparatus that are highly eflicient, particularly for producing low temperatures.

A further object of the invention is to provide a multistage mechanical refrigerator wherein operation of each stage can be optimized for the temperature produced at that stage.

Another object of the invention is to provide a multistage mechanical refrigerator of the above character in which the working fluid for each stage can be selected for optimum performance according to the temperature of the stage.

It is also an object of the invention to provide a multistage refrigerator of the above character that i operable with only two actuating motions.

The invention also comprehends the provision of a simple mechanical linkage for operating a refrigerator 0f the above character.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatu embodying features of construction, combinations of elements and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a simplified vertical cross section of a threestage refrigerator embodying the invention;

FIG. 2 is a graph showing the relative positions of the two actuating members of the refrigerator of FIG. 1 for one operating cycle;

FIG. 3 is a schematic representation of a mechanical linkage for producing the actuating motion for operating the refrigerator of FIG. 1; and

FIG. 4 schematically portrays, the operation of the refrigerator of FIG. 1 for a full cycle.

In general, a refrigerator embodying the invention has a plurality of stages, each of which comprises a pair of opposed cylinders fitted with a double-ended piston. One cylinder and one end of the piston form a high temperature portion of the stage and the other cylinder cooperates with the other end of the piston in the low temperature portion. The piston and cylinders define chambers at opposite ends of the piston. A regenerator communicates between the ends of the piston to allow the working fluid, i.e., the refrigerant, to transfer from the chamber at one end of the piston to the chamber at the other end thereof. Two actuating members move the parts of each stage independently with respect to each other, i.e., one of the parts is fixed and the other two undergo independent motion. For example, the two cylinders or the piston and one cylinder may move. Two moving parts preferably have a fixed relative phase between their motions.

The refrigeration cycle in each stage can be assumed to begin with movement of two parts, for example, the low temperature cylinder and the double-ended piston, to compres the refrigerant in the chamber at the high temperature portion of the stage, thereby heating the refrigerant. A heat exchanger transfers the heat away from the compressed refrigerant to a heat sink, thereby lowering the temperature of the refrigerant to that of the sink. The cylinder then moves to expand the chamber at the other end of the piston and thus draw the compressed refrigerant through the regenerator to the low temperature portion of the stage and allow it to expand, whereby it cools, absorbing heat from the low temperature portion of the stage.

The refrigeration cycle continues by transferring the cooled refrigerant, without compressing it, back through the regenerator to the high temperature portion of the stage. The refrigerant lowers the temperature of the regenerator in passing through it. At this point, the refrigeration cycle is complete, having decreased the temperatures of the regenerator and the low temperature portion of the stage. The next refrigeration cycle begins by again compressing the refrigerant at the high temperature portion of the stage.

The adjacent second stage of the refrigerator ha its high temperature portion in thermal communication with the low temperature portion of the first stage to maintain the temperature difference between them small.

The actuating mechanism operates the second stage with a sequence similar to that of the first stage, compressing its refrigerant in the high temperature portion and expanding it in the low temperature portion. However, since the high temperature portion of the second stage is maintained at nearly the same reduced temperature as the low temperature portion of the first stage, its compressed refrigerant is essentially at the low temperature produced in the first stage. Accordingly, expansion in the second stage cools the refrigerant therein to below the low temperature of the first stage. Thus by maintaining the high temperature portion of each succeeding stage at substantially the same temperature as the low temperature portion of the preceding stage, the refrigerator produces a succession of progressively lower temperatures. In this manner, the refrigerator efii-ciently produces very low temperatures.

The actuating mechanism preferably operates the multiple refrigerator stages with a fixed phase between the operation of adjacent stages so that as the refrigerant in the first stage expands, cooling the low temperature portion, the second stage compresses refrigerant in its high temperature portion, which is in thermal communication with the low temperature portion of the first stage. As a result, the heat produced in the high temperature portion of each stage is efficiently removed to the low temperature portion of the preceding stage to provide the overall temperature reduction of the system.

Turning now to FIG. 1, the illustrated refrigerator has three stages indicated generally at 10, 12 and 14, each stage having a high temperature end and a low temperature end. The stage comprises a double-ended piston 16 slideably interfitting at the high temperature end 10a in a cylinder 18 and at low temperature end 10b in a lcjylindzer 20 formed by a double-ended cylinder mem- The cylinder member 22 also forms a cylinder 24 that receives one end of a double-ended piston 26 in the high temperature end 12a'of stage 12. At the low temperature end 1219, the piston 26 fits in a cylinder 28 again formed by a double-ended cylinder member as indicated at 30. In the high temperature end 14a of stage 14, an end of a double-ended piston 32 fits in a cylinder 34 formed by the member 30. The piston 32 fits in a cylinder 36 at the low temperature end 14b of this stage.

The cylinders 18 and 36 and the piston 26 are fixed to a suitable support structure, as indicated schematically by the supports 68, 70 and 72. An actuating member 38 links the piston 16 and the cylinder member for unitary motion, and an actuating member 40 constrains the cylinder member22 to move with the piston 32. Bearings 42, 44, 46 and 48 support the actuating members 38 and 40 for reciprocal movement in the vertical direction (FIG. 1). In the cylinder members 22 and 30, thin walls 50 and 52 maintain a minimal temperature difference between their opposed surfaces and hence between the ends of cylinders 22 and 24. and cylinders 28 and 34 respectively. These walls are thin and of high heat conductive material so as to provide rapid thermal flow from one side to the other. The wall 54, forming the top of the cylinder 18, provides low resistance to heat flow from the high temperature end 1001 of the stage 10 to a heat exchanger 56 that is in thermal communication with a heat sink, -e.g., the environmental atmosphere as shown. Similarly, the wall 58 at the bottom of the cylinder 36 provides for efficient heat transfer from the low temperature end "of stage 14 to a heat absorber 60, illustratively a heat exchanger that is to be maintained at a low temperature. As also shown in FIG. 1, the pistons 16, 26 and 32 include conventional regenerators 62, 64 and 66, respectively, extending between the piston ends. An eflicient regenerator is a device having a fairly high heat capacity, low axial thermal conductivity, large surface area and small free volume. In the present refrigerating system the regenerators are used as heat storage elements. They provide substantially unimpeded flow of the refrigerant between the high and low temperature ends of each stage during various portions of each refrigeration cycle.

Other than indicated above, the system is well insulated, particularly to allow a substantial temperature difference to exist between the high temperature and low temperature ends of each stage. For this purpose, the actuating members 38 and 40 are appropriately made of material having a low heat conductivity, and thermal insulation 38a and 40a may be disposed between the actuating members and the pistons and cylinder members to which they are connected. In addition, the support 68 for the cylinder 18, the support 70 for the piston 26 and the support '72 for the cylinder 36 may appropriately include thermal barriers and insulation (not shown) to maintain the various pistons and cylinder members at different temperatures.

Curves 138 and 140 of FIG. 2 graphically show the motion of the actuating members 38 and 40, respectively. The movements of these members above lowest positions are plotted along the vertical axis as a function of time, represented in degrees of each operating cycle. At the start of an operating cycle, designated as the 0 position, both members are at their lowest positions. They move up together as indicated by the curve sections 138a and 140a for a third of the operating cycle, to the position. During the middle third of the cycle, between the 120 and 240 positions, the member 38 remains at its highest position, while the member 40 returns to its lowest position. The member 40 remains down while the member 38 moves down during the last third of the cycle. Although the curves 138 and 140 are drawn for simplicity to show linear motion, this is not required. For example, the member 40 (FIG. 1) may undergo sinusoidal motion between the 0 and 240 positions on the graph.

Referring principally to FIG. 1 and FIG. 4, in the 0 position, shown in the left hand column of the table, the actuating members 38 and 40 position the piston 16 and the lower cylinder 20 of stage 10 in their lowest positions with substantially no compression space between them. Hence, essentially all of the refrigerant gas in stage 10 is in the chamber 11a at the high temperature end, i.e., between the piston 16 and the upper cylinder 18. The actuating members then move the piston 16 and cylinder 20 up together, to the 120 position of FIG. 4, to compress the gas in the upper chamber of stage 10. The temperature of the gas accordingly rises, but the conducting wall 54 and heat exchanger 56 (FIG. 1) remove the heat of compression from the gas so that it remains substantially at the environmental temperature of the heat sink.

Thereafter, while the actuating member 38 holds the piston 16 in its elevated position, the member 40 moves down, bringing the cylinder 20 down to the position shown in the third column (240) of FIG. 4. During this downward movement of cylinder 20, the compressed refrigerant gas at the upper end of the cylinder 16 passes through the regenerator 62 and expandsinto the newly expanded chamber 1117 between the lower end of the piston 16 and the wall 50. The temperature of the gas in the stage 10 cools in undergoing this expansion, and absorbs heat from the wall 50, which is adjacent to the high temperature end 12a of stage 12. The temperature of the gas in the low temperature end 1% is raised somewhat by this heat exchange, but the gas is still colder than it was prior to expansion, i.e., in the 120 position.

The piston 16 now moves down to the 360 position, shown in the right hand column of FIG. 4, while the cylinder 20 remains stationary. This motion contracts the lower chamber 11b, while simultaneously expanding the upper chamber 11a. As a result, the refrigerant gas passes upwardly through the regenerator 62 without undergoing expansion or compression. In moving through the regenerator, the cooled gas removes heat from the regenerator, decreasing its temperature. This completes the refrigeration cycle, and the stage 10 is positioned to commence the next cycle.

The refrigerator then repeats the cycle, moving thepiston 16 and cylinder 20 together from their position in the first column of FIG. 4 to compress the gas in the high temperature portion 10a, arriving at the position shown in the second column of the table. Simultaneously, the wall 54 and'the heat exchanger 56 remove the resultant heat of compression. The cylinder 20 then moves down to the position shown in the third column of FIG. 4, drawing the compressed gas. through the -regenerator 62 and allowing it to expand between the piston 16 and the cylinder 20. However, the now cooled regenerator 62 cools the compressed gas as it passes to the low temperature portion a, so that the resultant temperature of the gas after expansion is lower than before.

Furthermore, during the next passage of the gas upwardly through the regenerator 62, caused by movement of the cylinder upwardly to the position shown in the fourth column of FIG. 4, the gas cools the regenerator 62 to a lower temperature than previously. Thus, as the cycle is repeated, the regenerator 62, the low end 10b and the gaseous refrigerant in the stage 10 become colder and colder. This continues until a terminal temperature is attained.

The refrigerator stage 12, below the first stage 10 and comprising the piston 26 and the cylinders 24 and 28, operates in the same manner as the stage 10. That is, compression takes place at the high temperature end 12a, between the piston 26 and the cylinder 24, and expansion occurs at the low temperature end 12b, between the piston 26 and the wall 52. However, the cooled low temperature end of stage 10, being in thermal communication through wall 50 (FIG. 1) with the high temperature end of stage 12, removes the heat of compression from the stage 12 refrigerant. Hence, the wall 50 brings the compressed gas in stage 12 to a temperature close to the low temperature produced in stage 10. As a result, the expanding gas in stage 12 attains a temperature that is much lower than the low temperature produced in stage 10. In other words, the stage 10 de velops a temperature difference AT between its high and low temperature ends and the stage 12 develops a dif ference AT between its ends 12a and 12b. However, since the ends 10b and 12a are close in temperature, the refrigerator develops a temperature at the low temperature end 12b that is of the order of AT +AT degrees below the temperature of the heat exchanger 56 (FIG. 1) at the high temperature end 10a.

In like manner, the compressed gas in the bottom stage 14, comprising the piston 32 and the cylinders 34 and 36, is cooled by the expanded gas in the stage 12. As a result, upon expansion in the low temperature end 14b, the gas in the stage 14 attains an extremely low temperature.

Considering the multistage operation in greater detail, the two actuating members 38 and 40 (FIG. 1) operate the stages 10, 12 and 14 according to a fixed time sequence much the same as the different cylinders in an internal combustion engine. As depicted in FIG. 4, this sequence is preferably arranged so that the gas in the stage 10 is expanding, and hence cooling, at the same time that the gas in the stage 12 is being compressed. As a result, the expanding gas in the stage 10 rapidly removes heat, as it develops, from compression of the gas in stage 12. FIG, 4 indicates that the expansion in stage 10 and the compression in stage 12 both occur between the 120 and 240 positions in each cycle. Similarly, expansion in the stage 12 coincides with compression in the stage 14, occurring between the 240 and 360 positions.

Inasmuch as the two actuating members 38 and 40 (FIG. 1) operate all three stages of the refrigerator, its moving elements have the same stroke, i.e., the same vertical travel. However, the high and low temperature ends of each stage should have suflicient heat capacity to handle the heat load of the next lower stage portion, together with heat input from friction and infiow from the environment. Accordingly, the diameters of the cylinder 34 and the upper end of the piston 32 are selected for a heat capacity that is at least equal to the load presented to the end 14a by the end 145, plus losses. The diameters of the pistons and the cylinders of the remaining stages are similarly proportioned to the absolute temperature and pressure conditions each to provide the compression 6 temperature requirements of the stages below them and also to cover losses. Moreover, the gas in each stage is selected to undergo a large temperature drop upon expansion from the temperature at which it is compressed.

Other characteristics of the gas, or working fluid, that may be selected for optimum performance in each stage include its conductivity, density, specific heat and viscosity. A working fluid having a high heat conductivity over the range of temperatures it experiences in a stage enhances the transfer of heat between the fluid and the chamber walls in the stages high and low temperature ends. Moreover, the mass, and correspondingly the heat capacity, of a working fluid having high density are greater than for a fluid of low density.

Since the working fluid in each stage is constrained to remain therein, the regenerator material in each stage can also be selected to further enhance the refrigerators performance. Thus, the conductivity and the specific heat and geometry of the regenerator material are preferably selected according to the operating temperature range in the stage.

With the two ends of each piston having different diameters as shown in FIG. 1, the chamber at the high temperature end of each stage will have a larger volume than the chamber at the low temperature end. The effect of this volume difference will now be described with reference to the stage 10. Following compression in the high temperature end 10a, the refrigerant is allowed to expand in the chamber 11b (FIG. 4) at its low temperature end. When the expanded cooled refrigerant is then transferred to the larger-volume chamber 11a, the temperature of the refrigerant increases somewhat as it removes heat from the intervening regenerator 62. However, the warmer refrigerant reaching the chamber 11a has a larger volume than it had in the low temperature expansion chamber 11b, and thus, even with the increase in temperature, the presure is not increased. If the pressure were to increase, the increase would be transmitted to the gas in the chamber 11b, causing an increase in the temperature therein. Thus, the transfer of the refrigerant between the ends of each stage is preferably an essentially constant pressure operation.

The arrangement shown in FIG. 1 is particularly suitable when the same gas is used for a refrigerant in all three stages. The supports 68, 70 and 72 support the stages vertically in an insulated vessel indicated at 74 that is filled with the refrigerant at the mean working pressure of the stages. The gas stratifies, distributing itself with the cold gas at the bottom and warm gas at the top in such a way that there is little temperature difference between the parts of each stage and the gas. Thus there is minimal heat transfer between them. Slight leakage of gas between the piston and cylinders of each stage into the surrounding gas in the vessel 74 is compensated by gas leaking back into the cylinders when these internal pressures are below the mean pressure. Bafiies indicated at 76 in the gas space of the vessel enhance the stratification of the gas by preventing disturbances due to motion of the actuating members and the pistons and cylinder members.

FIG. 3 shows a mechanical linkage arranged to drive the actuating members 38 and 40 of FIG. 1 for the operation described above. A motor 78 rotates its shaft 78a in the clockwise direction of arrow 80. A pulley 82 keyed to the shaft rotates a crank 84 in the same direction by means of a belt 86 passing around the pulleys 82 and the crank 84 and over idlers 88 and 90. A second pulley 92 on the motor shaft is coupled via a belt 94, guided by idlers 96 and 98, to a crank 100 rotating in the same, clockwise, direction.

A rod 104 connects a crank pin 102 on the crank 84 to a slide 106 slideably mounted in a horizontal channel 108. A second rod 110 is pivoted at one end to the slide 106 together with the rod 104 and is pivotally connected at its other end to a slide 112 supported in a 7 vertical channel 114. The slide 112 is connected with the actuating member 38 to reciprocate it according to the curve 138 of FIG. 2.

More specifically, with the crank 84 in the position shown, corresponding to the position of FIG. 2 and FIG. 4, the slide 106 is slightly on the left of its extrerne right position and the slide 112 and member 38 are just above their lowest position. Clockwise rotation of the crank 84 moves the horizontal slide 106 to the left, thereby drawing up the slide 112 and the member 38. This motion continues, as shown in curve 138 of FIG. 2, until the crank rotates approximately 120 degrees from the position shown to bring the crank pin 102 to the position indicated at 102a. The horizontal slide 106 is then in its extreme left position and the slide 112 and member 38 are in their highest position. The linkage of FIG. 3 has now advanced the member 38 through a third of the refrigeration cycle, to the 120 position on the idealized curve 138 of FIG. 2.

Continued clockwise rotation of the crank 84, revolving the crank pin for 120 degrees from the position 102a to the position 102b, pushes the horizontal slide 106 to the right, causing it to drive the vertical slide 112 and member 38 down. This motion corresponds to the middle third of the refrigerating operating cycle, between the 120 and 240 positions indicated in FIG. 2 and FIG. 4.

During continued clockwise rotation of the crank 84 for 120 degrees, from the position where the crank pin is at 102b, the rod 104 is substantially horizontal and it and the slide 106 experience little lateral movement. At the same time, the rod 110 is substantially vertical, so that movement of the rod 110 to the left or right causes little vertical movement of the slide 112. Preferably, the length of the rod 104 is such as to move the rod 110 slightly to the right of the vertical position when crank pin is at the extreme position shown at 102a. Thus the rod 110 moves back and forth closely about the vertical position as the crank pin progresses from 102b to 102. With this combination of rod orientations, the slide 112 remains relatively stationary, as shown in the portion of curve 138, FIG. 2, between the 240 and 360 positions.

It is thus seen that during a full revolution of the crank 84, the linkage of FIG. 3 drives the actuating member 38 through a full cycle of refrigerator operation.

As also shown in FIG. 3, the crank 100 similarly has a crank pin 116 to which is pivoted a rod 118 pivotally connected to a horizontal slide 120 in a channel 122 that may be an extension of the channel 108. A rod 124 pivotally connected to the slide 120 and also to a vertical slide 126 disposed in a vertical channel 128. The slide 126 is connected to reciprocate the actuating member 40.

The slide 126 is disposed in the channel 128 on the other side of the horizontal channel 122 from the vertical slide 112. Also, the rods 104 and 118, respectively, are pivoted to the cranks 84 and 100 at points spaced 120 apart. That is, the position of the crank pin 116 corresponds to the position of crank pin 102 if the crank 100 were advanced 120 degrees, relative to the crank 84. This arrangement of the linkage results in the phase relation shown in the curves of FIG. 2 between the motions of the mechanisms 38 and 40.

More specifically, in the position shown in FIG. 3, corresponding to the 0 position of FIG. 2 and FIG. 4, the vertical slide 126 is in its lowest position. As with the crank 84 and the linkage elements connected therewith, clockwise rotation of the crank 100 through 120 degrees from the position shown to the position where the crank pin 116 is oriented at the position 116a, drives the slide 120 to the left, causing it to push up the slide 126 and the actuating member 40.

' Rotating the crank 100 for a further 120 degrees, to orient the crank pin at the position 11 b, moves t e rod 118 about its horizontal position and while the rod 124 moves about its vertical position. As a result, the member 40 remain essentially stationary, in its highest position during this motion.

Continued rotation of the crank for 1'20 degrees, to dispose the crank pin in the position 116c, draws the slide 120 backv to the right, moving the slide 126 down again. This completes one revolution of the crank 100 and one cycle in the movement of member 40.

In summary, I have described a novel multiple stage mechanical heat pump illustrated as a refrigerator for producing low temperatures. Each stage of the heat pump has a double-ended piston fitted in two opposed cylinders with two of these three parts being independently moveable to alternately compress refrigerant in a high temperature end of the stage and then expand it at a low temperature end. The lubricant in each stage is isolated from the other stages, while the low temperature end of each stage is in thermal communication with the high end portion of the next stage in the direction of decreasing temperatures. Thus, the lubricant and refrigerant, as well as the regenerator, for each stage can be independently selected for optimum performance according to the temperature range of the stage.

The refrigerator can be constructed with a plurality of stages; yet only two actuating motions are required to operate it. Each stage can be considered as being the heat sink for the stage below it and the heat source for the stage above it.

The heat pump can also be operated as a workproducing heat engine by delivering heat to the bottom of cylinder 36 (FIG. 1) and removing heat from the top of cylinder 18. The resultant expansion and contraction of the refrigerants will drive the actuating members 38 and 40 in accordance with graphs of FIG. 2.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained, and since certain changes may be made in carrying out the above method and in the construction set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which as a matter of language, might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. A heat pump comprising in combination (A) first and second mechanical heat pump stages, each stage having a low temperature portion and a high temperature portion,

(1) each stage (a) substantially confining a working fluid therein, and (b) being operable to compress the working fluid therein, thereby heating the fluid, in the stages high temperature portion and expand the working fluid, thereby cooling it, in the stages low temperature portion, (2) said low temperature portion of said first stage being in close thermal relationship with said high temperature portion of said second stage, and (3) said high temperature portion of said first stage being thermally isolated from said low temperature portion of said second stage,

(B) first heat exchange means in thermal communication with said high temperature portion of said first stage to remove heat therefrom,

(C) second heat exchange means in terrnal communi- 9 cation with said low temperature portion of said second stage to transfer heat thereto, and

(D) actuating means (1) connected with said stages,

(2) successively operatiing each stage to alternately compress the working fluid therein and to expand the compressed working fluid, and

(3) operating said stages according to a fixed sequence wherein expansion in said first stage occurs at substantially the same time as compression in said second stage.

2. A multiple stage refrigerator comprising in combination (A) a first heat exchanger for transferring heat to a heat sink,

(B) a second heat exchanger for absorbing heat from a heat source,

(1) said first and second heat exchangers being thermally insulated from each other,

(C) at least first and second mechanical refrigerator stages, each stage comprising (1) a double-ended piston,

(2) a regenerator communicating between the ends of said piston,

(3) a high temperature cylinder slideably accommodating one end of said piston and forming a compression chamber therewith, and

(4) a low temperature cylinder slideably accommodating the other end of said piston and forming an expansion chamber therewith,

(5) said high temperature cylinder of said first stage being in a close heat transfer relation with said first heat exchanger,

(6) said low temperature cylinder of said first stage being in a close heat transfer relation with said high temperature cylinder of said sec ond stage,

(7) said low temperature cylinder of said second stage being in a high heat transfer relation with said second heat exchanger, and

(D) an actuating mechanism connected with said stages and (l) successively diminishing the compression space in each stage for compressing a refrig erant therein to heat it and increasing the expansion space to expand compressed refrigerant and thereby cool it.

3. The refrigerator defined in claim 2 in which said actuating mechanism operates said refrigeration stages according to a fixed sequence wherein expansion in said first stage coincides with compression in said second stage.

4. The refrigerator defined in claim 2 (A) further comprising support means maintaining said high temperature cylinder of said first stage and said piston of said second stage stationary with respect to said actuating mechanism, and

(B) in which said actuating mechanism comprises first and second reciprocating members,

(1) said first reciprocating member being connected with, and simultaneously driving, said piston of said first stage, and said low temperature cylinder of said second stage, and

(2) said second member being connected with, and simultaneously driving, said low temperature cylinder of said first stage and said high temperature cylinder of said second stage.

5. The refrigerator defined in claim 4 in which said actuating mechanism further comprises (A) a mechanical power source, and

(B) a linkage driven by said source and connected with said reciprocating members, said linkage reciprocating said members according to a fixed sequence wherein, in succession:

(1) said members translate together in a first direc- '10 tion from a first position to a second position,

(2) said first member dwells in said second position while said second member translates in the direction opposite to said first direction to said first position, and

(3) said first member translates from said second position to said first position while said second member dwells in said first position.

6. A multiple stage mechanical heat pump having at least first and second stages, each stage having a working fluid and being operable to compress said fluid and thereby heat it and to expand the compressed fluid and thereby cool it,

(A) each stage having a first portion in which its working fluid is compressed and a second portion in which its working fluid is expanded,

(B) heat conductive means (1) maintaining a minimal temperature difference between said second portion of said first stage and said first portion of said second stage, and

(2) transferring the heat produced in said second stage during compression of the working fluid therein to the expanded working fluid in said first stage, and

(C) actuating means (1) operating each stage to successively compress its working fluid in its first portion, transfer the compressed working fluid to the second portion thereof for expansion, and return the expanded working fluid to the first portion thereof for subsequent compression, and

(2) synchronizing the operation of said stages so that compression in said second stage substantially coincides timewise with expansion in said first stage.

7. A multiple stage mechanical refrigerator having at least first, second and third stages, each stage having a gaseous refrigerant and being operable to compress the refrigerant and thereby heat it and to expand the refrigerant and thereby cool it,

(A) each stage constraining the refrigerant therein from passing to another stage,

(B) each stage having a "high temperature portion in which its refrigerant is compressed and a low temperature portion in which its refrigerant is expanded,

(C) each stage having a regenerator communicating between its high and low temperature portions,

(D) said high temperature portion of said first stage being thermally isolated from said low temperature portion of said second stage,

(E) heat conductive means (1) maintaining a minimal temperature difference between said low temperature portion of said first stage and said high temperature portion of said second stage,

(2) maintaining a minimal temperature difference between said low temperature portion of said second stage and said high temperature portion of said third stage,

(3) transferring the heat produced in said third stage during compression of the refrigerant therein to the expanded refrigerant in said second stage, and

(4) transferring the heat produced in said second stage during compression of the refrigerant therein to the expanded refrigerant in said first stage,

(P) each stage compressing the refrigerant therein at a temperature corresponding to the temperature to which the refrigerant cools during expansion, and

(G) actuating means (1) operating each stage to successively compress its refrigerant in its high temperature portion, transfer the compressed refrigerant via the regenerator for expansion in its low temperature portion, and return the expanded refrigerant via its regenerator to its high temperature portion for subsequent compression, and

(2) synchronizing the operation of said stages so that compression in said second and third stages effectively coincides with expansion in said first and second stages, respectively.

8. A refrigerator as defined in claim 7 further characterized in that the transfer of refrigerant from the low temperature portion to the high temperature portion in each stage is a substantially constant pressure transfer.

9. A heat pump comprising in combination (A) first and second mechanical heat pump stages, each stage having a low temperature portion and a high temperature portion,

( 1) each stage comprising (a) a double-ended piston,

(b) a pair of opposed cylinders slideably accommodating the ends of said piston to form chambers therewith, one compression chamber being in the low temperature portion and the other being in the high temperature portion of the stage, and

(c) regenerator means for transferring working fluid between said chambers of the stage,

(2) each stage (a) substantially confining a working fluid therein, and

(b) being operable to compress the working fluid therein, thereby heating the fluid, in the stages high temperature portion and expand the working fluid, thereby cooling it, in the stages low temperature portion,

(3) said low temperature portion of said first stage being in close thermal relationship with said high temperature portion of said second stage, and

(4) said high temperature portion of said first stage being thermally isolated from said low temperature portion of said second stage,

(B) first heat exchange means in thermal communication with said high temperature portion of said first stage to remove heat therefrom,

(C) second heat exchange means in thermal communication with said low temperature portion of said second stage to transfer heat thereto, and

(D) actuating means connected with said stages and successively operating each stage to alternately compress the working fluid and to expand the compressed working fluid.

10. A heat pump comprising in combination (A) at least first and second mechanical heat pump stages, each stage having a low temperature portion and a high temperature portion, (1) each stage comprising (a) a double-ended piston (b) a pair of opposed cylinders slideably ac- I commodating the ends of said piston to form chambers therewith, one compression chamber being in the low temperature portion and the other being in the high temperature portion of the stage, and

(c) regenerator means for transferring working fluid between said chambers of the stage,

(2) each stage being operable to compress working fluid therein, thereby heating the fluid, in the high temperature portion of the stage and expand compressed working fluid, thereby cooling it, in the low temperature portion of the stage,

(3) said low temperature portion of said first stage being in close thermal relationship with said high temperature portion of said second stage,

(B) actuating means connected with said stages and successively operating each stage to alternately compress the working fluid and to expand the compressed working fluid, said actuating mechanism comprising (1) a first reciprocating member connected to drive said piston of said first stage and said low temperature cylinder of said second stage, and

(2) a second reciprocating member connected to drive said low temperature cylinder of said first stage and said high temperature cylinder of said second stage, and

(C) support means maintaining said high temperature cylinder of said first stage and said piston of said second stage stationary with respect to said members of actuating mechanism.

References Cited by the Examiner UNITED STATES PATENTS 1,808,494 6/1931 Carney 62335 1,929,307 10/1933 Castro 74--44 2,680,956 6/1954 Haas 62175 2,907,1'75 10/1959 Kohler 626 2,924,106 2/1960 Bohm 7444 3,091,092 5/1963 Dros 62--6 3,115,014 12/1963 Hogan 626 3,115,015 12/1963 Hogan 626 3,128,605 4/ 1964 Malaker 626 WILLIAM J. WYE, Primary Examiner. 

1. A HEAT PUMP COMPRISING IN COMBINATION (A) FIRST AND SECOND MECHANICAL HEAT PUMP STAGES, EACH STAGE HAVING A LOW TEMPERATURE PORTION AND A HIGH TEMPERATURE PORTION, (1) EACH STAGE (A) SUBSTANTIALLY CONFINING A WORKING FLUID THEREIN, AND (B) BEING OPERABLE TO COMPRESS THE WORKING FLUID THEREIN, THEREBY HEATING THE FLUID, IN THE STAGE''S HIGH TEMPERATURE PORTION AND EXPAND THE WORKING FLUID, THEREBY COOLING IT, IN THE STAGE''S LOW TEMPERATURE PORTION, (2) SAID LOW TEMPERATURE PORTION OF SAID FIRST STAGE BEING IN CLOSE THERMAL RELATIONSHIP WITH SAID HIGH TEMPERATURE PORTION OF SAID SECOND STAGE, AND (3) SAID HIGH TEMPERATURE PORTION OF SAID FIRST 